The preferred embodiments relate generally to a method and material composition for introduction into a hollow anatomical structure (HAS) with particular relevance to the venous system in the lower extremities. The term “hollow anatomical structure” is a broad term and is used in its ordinary sense, including, without limitation, veins, arteries, gastric structures, coronary structures, pulmonary structures, tubular structures associated with reproductive organs, and the like. Hollow anatomical structures particularly suited to occlusion by the methods of preferred embodiments include veins, preferably veins of the lower extremities, especially veins in the leg.
The human venous system of the lower extremities consists essentially of the superficial venous system and the deep venous system with perforating veins connecting the two systems. The superficial system includes the long or great saphenous vein and the small saphenous vein. The deep venous system includes the anterior and posterior tibial veins which unite to form the popliteal vein, which in turn becomes the femoral vein when joined by the short saphenous vein.
The venous system contains numerous one-way valves for directing blood flow back to the heart. Venous valves are usually bicuspid valves, with each cusp forming a sack or reservoir for blood. Retrograde blood flow forces the free surfaces of the cusps together to prevent continued retrograde flow of the blood and allows only antegrade blood flow to the heart. When an incompetent valve is in the flow path, the valve is unable to close because the cusps do not form a proper seal and retrograde flow of the blood cannot be stopped. When a venous valve fails, increased strain and pressure occur within the lower venous sections and overlying tissues, sometimes leading to additional, distal valvular failure. Two venous conditions or symptoms which often result from valve failure are varicose veins and more symptomatic chronic venous insufficiency.
The resulting condition is progressive and includes: dilation and tortuosity of the superficial veins of the lower limbs, unsightly discoloration, pain, swelling, and possibly ulceration. This failure can also worsen deep venous reflux and perforator reflux. Current treatments of venous insufficiency include surgical procedures such as vein stripping, ligation, RF ablation, laser treatment, vein closure, and vein-segment transplant.
Vein stripping and vein-segment transplant are less-favored treatment options. Vein stripping typically consists of tying off, or ligating, and removal of the saphenous vein. The ligation involves making an incision in the groin and using sutures outside the vein to tie it shut. When the veins are tied off and/or removed, blood flows through the deep veins and back to the heart. This surgery is generally done under general or spinal anesthesia during a hospital stay or on an outpatient basis, depending upon the extent of the procedure. Vein stripping is generally painful and requires a long recovery time. This procedure is less favored and outcomes can be poor. Procedures combining ligation and stripping are sometimes performed, but studies have shown they offer little advantage over stripping alone. Vein segment transplant has been employed in certain organ transplant procedures. However it is not generally employed in the superficial venous system in humans.
Ligation by ablation involves the cauterization or coagulation of vascular lumina using thermal energy applied through a delivery catheter, e.g., electrical energy applied through an electrode device (e.g., a radio frequency or RF device), energy delivered by regular and high-frequency ultrasound, or laser energy. An energy delivery device is typically introduced into the vein lumen and positioned so that it contacts the vein wall. Once properly positioned, the RF, laser, ultrasound, or other energy is applied to the energy delivery device, thereby causing the vein wall to shrink in cross-sectional diameter. A reduction in cross-sectional diameter, for example, from 5 mm (0.2 in) to 1 mm (0.04 in), significantly reduces the flow of blood through the vein and results in an effective ligation. Though not required for effective ligation, the vein wall can completely collapse, thereby resulting in a full-lumen obstruction that blocks the flow of blood through the vein.